Violent Vibration now no start

Posting this because I have absolutely no clue at this point;

Drove my car roughly about a week ago, noticed I was loosing speed and pulled off the freeway, as I slowed down to about under 25 noticed a sort of hard vibration/thumping sort of noise from under the car. Shut the car off and tried to see if I can physically see anything but nothing visible. Went to start the car and no start, it was like the battery was slowly dying but still trying to turn over. Called and got and got a jump, still didn’t turn over only to find out the theft light was the culprit, had it towed home that night.

Bringing it to today, got the battery charged and went to start it, started up first go but started low rpm and slowly slowly began to creep up to normal cold start rpm, and again, had that violent vibration, shut it off and started it again, same thing happened. Tried to start it a 3rd time and didn’t turn over or try, it just gave me one click. Despite having the battery fully charged.

cars a 2002 mustang gt nothing done aside from a CAI.
thanks I’m advance!

HemiRick said:

If with engine alone running and the car not driving, you have a bad vibration, it's obviously the engine....You need to figure out if its simply missing or has thrown a rod or something else really bad....Do you know how to do a compression test? if not learn.

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after doing some research, my guess is you may be right, it might've thrown a rod/spun a rod bearing. Won't be 100% sure until I get it towed to a mechanic, won't be surprised honestly, whoever had the car before really really didn't take care for it at all.