He was a willing accessory to the predicate act of breaking and entering. A man died as a consequence of the chain of events that resulted from that criminal act. Therefore, he was guilty of murder.
Maybe under U.S criminal law (which I'm not very familer with) but certainly not under criminal law over here; the
actus reus of any homicide is an act or omission that directly leads to death (in the '50's the year and a day rule was still in place, but that's irrelevent to this case), while the
mens rea of murder is "malice aforethought" (ie; either intent to kill, intent to cause grievous bodily harm, realizing while doing something that death would almost certainly (or very probably) result, or realizing that grievous bodily harm will very probably result from the act... for example shooting at someone without intending to kill, but realizing that he'll suffer a serious injury). It's quite absurd to think that Bentley had committed the
mens rea of murder (the conviction only happend due to what increasingly looks like fabricated evidence on behalf of the police and the appalling conduct of the trial by the Judge... a depraved individual who got a sexual thrill from sentencing people to death*) and it's equally absurd to think that, beyond all reasonable doubt, he committed the
actus reus of homicide either. It might be possible to stretch out a manslaughter conviction (although even then it would be pushing the law to breaking point) but the most he would be charged with these days would be burglary.
*I can go into details here, but I'd rather not...