HUPD officers said they believe the most recent assault is linked to six other robberies in the area over the last week.
"The proximity of the crimes, the similarity in descriptions of age and clothing and the timing make it very unlikely for these to be different groups of perpetrators," said HUPD Sergeant Robert A. Cooper.
Based on victims' accounts, HUPD describes the robbers in last week's assaults as four black males, aged 17 to 20. HUPD estimates that three of robbers are about 5'8" tall, and the fourth is 6'2".
HUPD officers said they believe that some of the same men have been involved in each of the attacks, though several robberies have involved more than four assailants.
Cooper said he believes the robbers may be from outside the area. He said he believes they may have a false sense of security because they have found victims with relative ease.
"The robbers are usually stupid enough to keep coming back until they get caught," Cooper said.