Fire and building officials are continuing an investigation Tuesday into the cause of a Bronx store blaze that killed two firefighters.Sunday's fire started behind refrigerator closets at a 99-cent store on Walton Ave, where a fire also took place in 2000. After that fire the owner made repairs to the building?s joists and partitions. Fire officials say it?s too soon to tell whether the repairs contributed to Sunday?s blaze, which does not appear to be suspicious. From 1978 through 2000, records show building inspectors found nine safety violations at the site. Most of the violations were later dismissed.Firefighters Michael Reilly, 25, and Lt. Howard Carpluk, 43, died after the store?s first floor collapsed, propelling the two into a basement where they were buried under debris.