PHILADELPHIA (AP) -- Philadelphia police say two 13-year-old boys blackmailed an 11-year-old girl to force her to make a sex video with them. Police say the boys forced the girl to make the video with them on Oct. 8 near Tilden Middle School in southwest Philadelphia. The boys then allegedly posted the video online. Authorities say the boys were taken into custody Friday afternoon to be charged with various sex offenses. All three are students at the school. Police were alerted to the video by the school's principal, who says a student saw it online and brought it to his attention. Authorities say a third boy may have been involved but he hasn't been found.