A pawn shop tip leads the police to a gun used in a recent liquor store hold-up. The retrieved bullets match exactly those pumped into Cullen's lover's husband. Cullen is gob-smacked, after all hadn't he personally thrown the gun from the Golden Gate Bridge into the depths of the bay?
Then ... Cullen and brother Andy follow up the lead, interviewing the fisherman whose wife had pawned the gun. In one of of those happenstances that any noir movie worth its salt simply has to have, it turns out he had snagged the gun in his net.
... and Now, this was filmed at the north edge of the Fisherman's Wharf harbor (map). in both images we see a boardwalk mid-harbor and beyond that the neighborhood rises to the top of Russian Hill.
... and Now, an aerial view, the arrow marks the spot where the movie camera filmed the scene, aimed across the harbor in the direction of the arrow.
... the same aerial view in 1951, In the vintage photo below note that when the movie was filmed the boardwalk connected across the harbor via a footbridge, since removed. On a trivia note, the 1950 San Francisco movie Woman On The Run did a location shoot on this same boardwalk.
Then ... The detectives take the fisherman to his house to interview the wife - they are seen here on the steps leading to both of the gabled houses; it isn't made clear which of them was meant to be the fisherman's place because the scene faded out at this point but CitySleuth opts for the upstairs unit of the smaller one, given his modest income. This is 287A Union Street (map) just above the Calhoun Terrace cul-de-sac near the top of Telegraph Hill.
... and Now, these historic houses (amongst the lucky few at the top of Telegraph Hill that narrowly escaped the 1906 fire) have since seen a number of changes. The stairs have been redesigned, almost hiding the smaller gable from this angle, and the house with the taller gable, number 289, has gained height. Again, coincidentally, these same houses also made an appearance in Woman On The Run. The boxy apartment building now on the corner of Calhoun Terrace was built on the site of the notorious bohemian Hoeffler compound, the revolving-door home to artists and writers in the early 20th century.
Then ... Inside the house the wife swears up and down that nobody else had seen the gun before she pawned it, but concedes they have a 20 year old unemployed son living with them. This scene was obviously filmed on a studio soundstage because the view from their window is from a completely different location. Fortunately CitySleuth recognized it.
... and Now, that gabled building is the Brocklebank Apartments at 1000 Mason Street on Nob Hill, famously the home of Kim Novak's mysterious Madeleine in the 1958 classic Vertigo. Based on the direction and angle, this view must have been taken from the roof of the Bently Nob Hill apartments at 1360 Jones Street. CitySleuth was once on that roof to match another rooftop shot from 1947's The Lady From Shanghai) but he got this close match from 1310 Jones on the same block.
... and Now, in a reverse view this recent photo of Nob Hill taken from the Hilton Hotel at Portsmouth Square shows 1360 Jones (arrow at right) and the Brocklebank (arrow at left). Back in 1950 when the movie was filmed 1360 Jones and its highrise neighbor at 1250 Jones - the taller one with the mast - punctuated the skyline as lone sentinels with no other tall buildings around them.
    Helen Brent from San Francisco has just spent six weeks in Reno to meet the Nevada state residency requirement for a divorce.
Then ... The movie opens with a shot of Reno's iconic arch spanning Virginia Street at Commercial Row (map).
... and Now, the arch has undergone changes over the decades. Here it is today, the third version since it was originally installed in 1926.
Then ... The camera looks south down Virginia Street with casinos, cafes and bars lining the street on both sides. The Riverside Hotel faces us from the other side of the Truckee River where Virginia Street chicanes around to the left. That's the shadow of the arch in the near foreground.
... in the 1950s ... a picture postcard view taken a few years later shows the same scene in glorious color. Additional casinos have appeared by this time, undoubtedly the heyday of the Reno strip.  The Riverside then was the hotel of choice by the well-heeled for their six week divorce residency.
... and Now, Harolds Club and the Nevada Club on the left are gone now, victims of the competitive success of rival Harrah's and other newer, flashier casinos. The Riverside Hotel building is still there although the hotel closed in 1987, eventually replaced by retail stores and artists' lofts.
Then ... Helen and her attorney emerge from the courthouse.
... and Now, this is the Washoe County Courthouse on Virginia Street a few blocks south of the Reno Arch (map), still there and still in use. It was built in 1911 with a neo-classical design that incorporated the original 1872 courthouse within it.
 Helen (Claire Trevor) thanks the attorney for securing her divorce and bids him goodbye. Her smart outfit is the first of many that she wears with style throughout the movie. A classy dame to be sure but as we shall see, this being the dark world of noir, she too has a dark side.
( A Bunker Hill movie in a San Francisco blog? CitySleuth explains why).
Homer and his buddies may spend all day hanging around at home but they usually go out at night. They deposit Yvonne at a local movie theater, the Roxie, before speeding off to hit the local 'Indian' bars.
Then ... This is the view looking north on Broadway towards 5th Street (map). The converging street lights, the highlighted tram rails, the flashing neon of three cheek by jowl movie theaters on the right, all add glitz to the scene. They are the Roxie, the Cameo and the Arcade, at 518, 528 and 534 S. Broadway.
... and Now, they say 'The Show Must Go On' but that's no longer true on Broadway, Los Angeles. All three theaters have closed but their marquees are still there, as too is the vertical rooftop Roxie sign. The tram tacks have long since been torn up.
Then ... In this shot in the opposite direction the Roxie and its neighbors are on the left.
... and Now, the harsh light of day and downtown changes over the decades - neon seems to be out of style theses days - have dimmed the excitement. At least the original twin-globe street lamps are still there
Then ... Yvonne buys a ticket at the Roxie's art deco booth. These shots were supposedly filmed on the same evening but the movie showing here is The Iron Sheriff from 1957 featuring Sterling Hayden whereas in the above view Lana Turner in Imitation Of Life from 1959 was on the bill, reflecting the extended period over which Kent MacKenzie filmed the movie.
... and Now, the lobby of the Roxie Theatre is presently a retail store. There are plans however to reopen it in a move towards revitalizing the neighborhood. Note the mosaic sidewalk pattern in front of the theater, still there after all these years.
Then ... As Homer and friends drive off we see Ohrbachs apparel store across the street and a Newberry dime store on the corner across 5th.
... and Now, the tenants and storefronts not surprisingly are different now.
When Yvonne leaves the theater she briefly waits but knows she isn't about to be picked up, left to find her own way home while the boys continue their carousing.
A liquor store owner has been shot in a robbery. The ballistics results show that the bullets match those that killed Frazer, but no gun has turned up. Cullen is understandably puzzled; after all, he tossed the gun from the Golden Gate bridge into the bay. He arranges to meet Lois at a park.
Then ... He makes his way up a path. Behind him a cable car rolls down the hill past a large mansion.
... and Now, this is Lafayette Park and the stately home is the Spreckels mansion at 2080 Washington Street (map), one of San Francisco's famous buildings and a city landmark. Sugar magnate Adolph Spreckels built the French Baroque limestone home in 1913 for his trophy wife Alma deBretteville. Alma was still living there when the movie was filmed; today it is the home of novelist Danielle Steel - she added the unsightly privacy hedge, below. The cable car rolls by no longer, this line having been discontinued six years later, in September, 1956.
Then ... Lois is waiting for him by a park bench. Across the street is the mansion's circular driveway.
... from the 1950s ... The over-the-top hedge now hides the driveway from this spot but this 1953 photo captures it. The original Washington Street entrance was abandoned in favor of the side entrance during Alma's tenure. Incidentally, the Spreckels mansion was featured two years later in the movie The Sniper and again five years after that in Pal Joey.
Then ... Cullen tells her about the latest ballistics evidence but she's more interested in asking him if he would marry her. Knowing she's been married twice before, he's reluctant to commit (er, and didn't she just shoot her last husband?). The view looks past Pacific Heights to Fort Mason and across the north bay to Alcatraz and Angel Island.
... and Now, Ms Steel's hedge is being sculpted but still gets in the way of the view across the Bay for passers-by at street level.