Authorities dismissed charges against a Twin Cities man accused of injuring an 81-year-old woman while trying to rob her outside a St. Paul drugstore late last year.

The defense of Isaiah J. Foster, 19, of Richfield successfully argued that he was in Bloomington the afternoon of the mugging at the entrance to the Walgreens in the 1110 block of Larpenteur Avenue early in the afternoon on Dec. 23.

Foster's mother turned in her son and told authorities that he was the suspect she saw in Walgreens surveillance video. However, the defense said the mother later retracted her statement.

Prosecutors in Ramsey County District Court dismissed the assault charges, explaining in its court filing that "the state cannot prove the charges beyond a reasonable doubt."

The woman who was attacked at the drugstore suffered a concussion and bleeding on the brain from the attack, and then had a dizzy spell while in the hospital, fell and broke her pelvis, the charges against read.

Foster is jailed in Hennepin County on charges involving two cases involving multiple armed robberies in December in Minneapolis. He's due in court on April 18.