Silent Hill Homecoming

The first Siam is in the parking lot of the police station. You can fight it right after the cutscene where it smashes the car with Elle in it.

Before you encounter the Siam, make sure you have at least 5 rounds of shotgun ammo. You can find some ammo and health in the locker (same room where you pull the lever to open the gate). Combination for opening the locker is 206.

Go under the garage door and pump some lead in this ugly ass Siam. Try to aim for the head.

Kill 1 Siam.

The first Siam you encounter will be in the Police Station parking lot, after you meet with Wheeler and trying to find Elle. You will have to kill this one to further the game.

There are only a handful of these monstrosites in the game, they are very powerful and super quick.

Their biggest weakness is the shotgun, you can fell one of these guys with 3-4 shots no matter where you hit it, as long as they are close enough (which they usually are :D)

If you don't have any shotgun ammo, use either your pistol or rifle (if you have it), they are somewhat weak to these weapons and will make them pause with every hit.

As a last result if you're out of ammo, use the Knife. Dodge its attacks and use quick counters and attacks, try and sidestep behind it to the female legs, attacking them will deal some heavy damage.

Here is a vid showing the 1st Siam of the game who makes an appearance just before the end of the sheriff station level, the best and quickest way to defeat the Siam is with a powerful weapon such as the shotgun or rifle which you get later in the game.

The first Siam you encounter will be in the Parking Lot of the Police Station. Kill it and the achievement will unlock.