12/20: Snowstorm causes travel headaches; remembering Sandy Hook's principal

During rush hour in Connecticut, two commuter trains collided, sending 72 passengers to the hospital. The tracks are now closed while the NTSB investigates. And as Don Dahler reports, it's creating a travel nightmare; And, after his close friend died from pancreatic cancer, 16-year-old Jack Andraka unleashed his hyper-drive intellect on preventing more cancer deaths. And as Jim Axelrod reports, the teen created a much faster and far cheaper detection method for pancreatic, ovarian and lung cancer.

Members of Congress grilled acting IRS commissioner Steven Miller about the agency's targeting of conservative groups. Nancy Cordes reports on the four-hour barrage of bipartisan disgust; And, Steve Hartman reports on how a school assignment to interview a vet turned into a personal mission to get him long-overdue recognition.

Twisters with winds of up to 200 miles per hour in north Texas left six dead, many injured and scores of homes destroyed in their wake; Then, the surviving Boston bombings suspect wrote a note inside the boat in which he was hiding, detailing the motive for the attack; Also, American combat troops are due to leave Afghanistan after next year and are training Afghans to take over security

Attorney General Eric Holder said IRS specialists may have violated avariety of laws when they singled out conservative groups for special scrutiny, starting in 2010; Also, Michelle Miller meets with one of the last victims still hospitalized after the Boston Bombings; And, Cicadas, after living underground on the East Coast for 17 years, are about to re-surface. They will be making plenty of noise -- and love.

The Treasury Department's inspector general released a report that faults "ineffective management" at the IRS, which caused "substantial delays" for tea party groups applying for tax exempt status; Also, the Justice Department collected phone logs for 20 telephone lines used by more than 100 reporters and editors in an investigation aimed at finding who inside the government leaked classified information to reporters at the Associated Press; And, one group of birdwatchers in Dearborn, Mich., takes a different approach on how to appreciate the beauty of winged wildlife.

Dr. Kermit Gosnell left the courthouse a convicted murderer, in a prison jumpsuit and handcuffs. Prosecutors said Gosnell delivered babies alive, then cut their spinal cords with scissors. He could learn next week if he'll get the death penalty or life in prison; also, as executive director of the Richmond, Va., Tea Party, Laurence Nordvig says he thought for two years the tea party had been singled out by the IRS for an unusual and highly political investigation; and a Cleveland police officer and a police dispatcher describe the discovery of Amanda Berry, Michelle Knight and Gina DeJesus inside the Cleveland horror house.