Wilshire Police Station
When you arrive, go to the officer at the front desk. He informs you that you are wanted in tech services. Go downstairs to meet Pinker. (There are signs on the wall for technical services if you need them.)
When you find Pinker, he will show you some photographs that you need to investigate. These are the photos:
1st photo: Phelps (no information)
2nd photo: Zoom in on the watch and ring.
3rd photo: Zoom in on Mapes’ tie pin.
4th photo: Zoom in on the notes.
5th photo: Zoom in on the two walking men.
6th photo: Zoom in on the house number.
After you are done looking at the photographs, Pinker wants you to do an experiment. Use the eyedropper to put a drop from each bottle into the petri dish. There will be a cut-scene showing Phelps being knocked to the ground by the explosion caused by the concoction.
After the cut-scene before you leave tech services, walk around the desk that has the photographs to the other magnifying glass. Use it to zoom in on the document there to get the clue: Aluminum polishing patent. Go to the House in the Photograph to continue the case.
House in the Photograph
Head inside the house, and investigate the gas on the floor. Walk into the area with a bed. At the foot of the bed there is a little table that has a ticket and a passport on it. Investigate them both, and then a molotov cocktail will be thrown into the house. Your partner Biggs instructs you to shoot the gas line by the stove (which is a large red tank). Shoot it and follow Biggs out of the house.
There will be a cut-scene, and then you have to chase Mapes by car. Pursue him to Hughes Aircraft on your first attempt to unlock the L.A. Noire Out Of The Frying Pan Achievement. Mapes will lead you through a few alleys and yards before getting onto a main road. When you are on the main road, some opposing vehicles will try to stop you. Give them a little nudge if you need to, and they shouldn’t give you much trouble. When you arrive, if you were able to apprehend Mapes in your first attempt, you will unlock the Achievement, and you will then have a shootout.