Radec is difficult to kill, especially if you are attempting to get the 
"Demonslayer" trophy for killing him in under twenty minutes. Do not worry about 
him until you get the cutscene where he says "I guess you want to make it 
personal!" In the beginning he will send hordes of Helgast troops at you. Just 
dig in, and kill them all. You will be on the ground floor for about three waves 
of troops. Then the doors on the side will open, allowing you to get to the 
balcony. Note: Ammunition is limited on the balcony; make your shots count. When 
you reach the balcony, there will be two flamethrower Helagst waiting. 
Afterwards, there will be two waves of infantry then a mixed group of infantry 
and knife wielding Helgast officers. Be careful because when you are on the 
balcony they will come up from both sides. Take care of them first, then focus 
on the floor troops. After this wave there will be RPG troops on the far wall of 
the room. Take them out, then go back to the floor troops. After about six 
waves, there will be another cutscene of Radec. You will now be back on the 
ground level. Radec will now phase in and out of invisibility, and appear beside 
you and try to knife you. Keep moving and shooting at him as he shows himself. 
After hitting him enough times, he will retreat to the stairs in front of you. 
Keep shooting him until he dies.
After Radec makes the comment about "making it personal", there will be waves of 
troops that keep appearing. There is no real strategy here other than "run and 
gun". When it gets down to just you and Radec, and he keeps turning invisible, 
stock up on ammunition (rifle recommended). Go up to the balcony, and put your 
back in a corner. Radec will not be able to sneak up on you. You only have to 
cover the left and right. You will hear him appear and see a flash of light to 
indicate which direction he is coming from. Occasionally he will appear on the 
ground floor. Peek over the rail and shoot him a few times, then get back to the 
corner. After a short while he will appear on the stairs. Keep shooting him 
until he dies.
Easy "Barrel Of Death" trophy 

Easy "Dragonslayer" trophy 

Easy "Fragmerchant" trophy 

Easy "Melonpopper" trophy 
When you cross the Salamun Bridge and lower it for the rest of your squad to 
cross, take the sniper rifle on the weapons rack. Walk out the door, but do not 
advance further down the bridge. Above the road is a turret with a gunner. Shoot 
him in the head, and wait a few seconds. Someone will replace him. Keep shooting 
them in the head until you get the "Melonpopper" trophy.