This is really scary!
When few person form a group and crime is committed by a group this section 149 applies.
It speaks about such unlawful assembly and “EVERYONE” in group is equally liable.
In 2010(9) Sclae 57, on page 59 in para 6, Supreme Court said,
“Where deep enmities is admitted with history series of murders and attempted murders interse, and political rivalaries going back for years together, a case of false implication is a clear possibility”
It is for these reasons, mere evidence of eye witness not enough. The court will look for some independent corroboration to what witnesses are saying.