The man suspected of shooting dead four people midtown Manhattan last month had years earlier threatened to kill himself as he dealt with depression and concussion symptoms, according to a phone call his mother made to police.

Crazed gunman Shane Tamura, who shot dead four people at a Midtown Manhattan office building before turning the gun on himself last Monday, suffered from a sports-related concussion and multiple alarming mental health episodes that led his mother to call 911 on him, according to new details released by authorities.

Workers returned to 345 Park Ave., on Monday​ under the watchful eyes of NYPD officers and a surplus of security after the NYC mass shooting.