Russian news agencies quote officials with the St. Petersburg prosecutor's office as saying the suspect -- a 28-year-old man -- was detained over the weekend. No charges have been brought against him yet.
Samba Lampsar Sall, a 28-year-old Senegalese student, was gunned down as he emerged from a nightclub on April 7.
St. Petersburg has been the site of several recent attacks on foreigners, mainly from Africa.
(RIA Novosti, ITAR-TASS)