PHILADELPHIA (AP) — Police in Philadelphia say a second suspect is in custody in the assault of a University of Pennsylvania graduate student who was hit with a brick.

A police spokesman said Saturday that 18-year-old Dajuan Dantzler turned himself in Friday night to face charges. Twenty-year-old Lance Ryan was arrested earlier and is charged with assault.

Authorities said a 26-year-old male graduate student beaten and robbed Nov. 5 was left with serious head injuries, including a fractured skull.

Investigators believe they may be tied to two similar robberies. Another person walking home from his bartending job the night before had been attacked and struck multiple times with a brick.

It's unclear whether Dantzler has an attorney; Ryan is represented by the public defender's office, which couldn't be reached for comment.