Ilyas Ilyasov was the third cleric attacked in 2013 in Makhachkala, the capital of the Russian North Caucasus' volatile republic, the Russian news agency RIA Novosti reported Saturday.
The officer said it was not known whether the killing was related to imam's line of work.
A rabbi was hospitalized with gunshot wounds in Derbent in July, and another imam was killed in Gubden in March, RIA Novosti reported.
Eight other Muslim clerics were killed in Dagestan in 2012. Most of those killed were opposed to Salafism, an ascetic, militant Islamic sect that wants to establish an independent Islamist state in the Northern Caucasus and other areas with large Muslim populations, the newspaper said.