"I opened the bag, (and) I saw the most money I ever saw in my life," 72-year-old MacCausland told WFXT. "(I thought), 'I can go back looking for him because I know he's going to be looking for me, or take it home, change my life, or go to the police station.'"
He then drove to police headquarters to turn in the cash.
The owner of the backpack called police and was able to provide proof of ownership. The man had reportedly just cashed in his inheritance.
The 46-year-old man gave MacCausland a $100 reward and, according to the Boston Globe, the driver won't have to pay rent on his cab this weekend.
"My mother always said, 'Do the right thing. You'll be rewarded somewhere later, you know?' Maybe she's right," MacCausland said.
This video includes clips from WBZ and WHDH. Music provided courtesy of APM Music.