Angel is a vampire. he's stong and fast. he killed people for pleasure for over a century. and the best way he could come up with to try to kill Wesley was to put a pillow over his face to smother him? Angel could have killed Wes quickly, in a blink. he didn't though. he also didn't need to shout and bring the orderlies and the rest of the gang running in. deep down, Angel didn't want to kill Wesley.