the stiff body was clearly not something that had just happened. the paint being on the floor was something that had just happened. reporter: and now prosecutors played their ace. they called a new witness to bolster their case, someone not heard from in previous trials. do you solemnly swear to reporter: engineer david guillianelli. he really did watch paint dry, conducting dozens of lab experiments. were you able to form an opinion as to that time frame when the paint might have hit the floor? yes. and what is your opinion? within approximately 30 minutes of the time the first responders arrived. reporter: the final coat of a slap-dash cover-up. but motivation. why did by most accounts, the more sensible one of the two, turn on her fiery partner? prosecutors said the seeds were planted some ten months earlier. and they played an audiotape from a contentious court hearing to prove it. i m not going to play games with this. reporter: it was may, 2009. ann and ca
masking the evidence, the prosecutors said, that paint pointed to cara s guilt. the stiff body was clearly not something that had just happened. the paint being on the floor was something that had just happened. reporter: and now prosecutors played their ace. they called a new witness to bolster their case, someone not heard from in previous trials. do you solemnly swear to reporter: engineer david guillianelli. he really did watch paint dry, conducting dozens of lab experiments. were you able to form an opinion as to that time frame when the paint might have hit the floor? yes. and what is your opinion? within approximately 30 minutes of the time the first responders arrived. reporter: the final coat of a slap-dash cover-up. but motivation. why did by most accounts, the more sensible one of the two, turn on her fiery partner? prosecutors said the seeds were planted some ten months earlier. and they played an audiotape from a contentious court hearing to prove it.
the stiff body was clearly not something that had just happened. the paint being on the floor was something that had just happened. reporter: and now prosecutors played their ace. they called a new witness to bolster their case, someone not heard from in previous trials. do you solemnly swear to reporter: engineer david guillianelli. he really did watch paint dry, conducting dozens of lab experiments. were you able to form an opinion as to the time frame when the paint might have hit the floor? yes. and what is your opinion? within approximately 30 minutes of the time the first responders arrived. reporter: the final coat of a slap-dash cover-up. but motivation. why did by most accounts, the more sensible one of the two, turn on her fiery partner? prosecutors said the seeds were planted some ten months earlier. and they played an audiotape from a contentious court hearing to prove it. i m not going to play games with this. reporter: it was may 2009.