Police in Detroit are searching for men who allegedly robbed couples in separate attacks and gang-raped the women while forcing their male victims to watch.

Police say the attacks happened late Thursday and early Friday on Detroit's west side. They say they believe at least one suspect took part in both attacks and have released sketches of him and two others.

They say six men took part in one attack, forcing the 18-year-old woman and 21-year-old man to strip at gunpoint before raping her and robbing them. They say four men took part in the other attack, in which the woman was also raped.

Police are investigating a July 11 attack in which two men robbed a couple and raped the woman. They haven't definitively connected it with the others.