I have quite a bit of experience with cycling in general mountain bikes especially. This bike got me stumped, it has a Titan racing stem, vintage Easton peregrine carbon str8 bars, Easton answer Manitou front shocks, headlock headset, deore LX groupset, and a seat post that has an "A" and a star and USA. The frame itself has a couple numbers under the bottom bracket but I haven't been able to come up with anything. Also on the under side of the down tube it has what appears to be an "easton" "E" stamped. Thanks for any insight!
My Google-Fu comes up with the 1991 Alpinestar Ti Mega. It looks like they made an aluminum version as well. The tube shapes look to be about the same. Might be a good starting point for you.
My friend had one, definitely Alpinestar. The forks are probably newer than '91, look like mid-90's Manitou's. The stock fork was probably rigid, someone swapped it out with the suspension fork.
Alpinstars or Nishiki are the only two manufacturers that I know of that made a frame like that.
Haro Extreme Fat chance yo eddy