Mark Sanchez spent about 20 minutes roaming and, at times, stumbling around downtown Indianapolis before the violent encounter with his alleged victim ... and this new video shows nearly all of his activity.

TMZ Sports obtained surveillance videos tracking the ex-NFL star -- from 12:05 AM, when the alleged victim, Perry Tole , pulled up in his service truck ... to 12:30 AM, when Sanchez fled the scene, bloodied from stab wounds.

When Tole arrives, you see him drive south down the alley ... where, apparently, Sanchez was already on the move. When Tole parks, he's out of camera view, so we don't know if they see each other, but 7 minutes later, Sanchez walks north out of the alley ... stumbling a bit.

He's not injured at this point, and doesn't seem agitated. TMZSports.com

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