or edr. >> in those kind of accidents edr data will be invaluable. >> reporter: sean dennis is a forensic engineer who reconstructs car crashes for law firms and insurance companies. >> it's hidden way up underneath the dash. >> yep. yep. yep. >> reporter: it is tied into the air bag system and records two to five seconds of pre-crash data, things like engine speed, throttle, brakes, accelerator, seat belts. >> we see here 2.3 seconds before -- before the crash this person, this driver has gone from brakes off to brakes on. >> chrysler, gm and ford give people like dennis access to information through a crash data reader anyone can buy. >> it's compatible with this particular system and toyota is not compatible with this system. >> toyota calls its black boxes, experimental and the data is only for research and