(CBS News) Tasers may provoke heart problems in the people it strikes, according to a new study from the American Heart Association’s journal Circulation.

VIDEO: Taser: An officer’s weapon of choice

The study of electronic control devices (ECDs) – often known as Tasers – was conducted by Dr. Douglas P. Zipes, a cardiologist at Indiana University, who gained unprecedented access to police, medical and emergency response records, autopsy reports, and data from defibrillators and electrocardiogram (ECG) strips. Zipes used all the materials to analyze eight cases where clinically healthy men lost consciousness after being struck by a Taser X26, and all but one died.

Violence erupted at Black Friday sales across the U.S. with one bargain-hunter left critically injured after being shot during a robbery and 15 other people injured when an angry shopper used pepper spray.

Several of the incidents took place at Wal-Mart stores as millions of Americans loaded up on holiday purchases.

Update 11:57 a.m. ET: An off-duty police officer used pepper spray on shoppers at a Wal-Mart in Kinston, N.C.

Kinston police Sgt. Roland Davis said an off-duty officer whom the store had hired to help with security used the chemical while trying to make an arrest during a disturbance. Unconfirmed reports said as many as 20 peopl ewer affected.

GREENVILLE, S.C. — A gunman fired on a South Carolina police officer checking on a suspicious license plate Friday, causing 10 schools in Greenville to go on lockdown.

The schools reopened their doors after a couple of hours and it
appears the gunman was able to get someone to pick him up and elude a
massive manhunt that went on for hours, authorities said.

Police identified the gunman as 25-year-old Patrick Dean Lowrance and
said he was wanted on attempted murder and other charges. They think he
might have been wounded when the Greenville officer fired back at him
and asked hospitals in the area to be on the lookout in case anyone came
in with a gunshot wound.

SEAL BEACH, Calif. — Six people were shot to death and three others wounded at a hair salon on Wednesday in a normally sedate Southern California beach community, Orange County authorities said. One suspect was in custody.

The shooting occurred at Salon Meritage around 1:30 p.m. in the 500
block of the Pacific Coast Highway, Capt. Mark Stone of the Orange
County Fire Authority told NBC LA.

Three victims were rushed to Long Beach Memorial Hospital, reportedly in critical condition.

Victims were believed to be both employees and customers of the salon, KTLA News reported.

BOSTON — A Massachusetts man was arrested and charged Wednesday with plotting to attack the Pentagon and U.S. Capitol with a remote-controlled aircraft filled with plastic explosives, federal officials said.
Rezwan Ferdaus, 26, of Ashland, was also charged with attempting to provide material support and resources to al-Qaida in order to carry out attacks on U.S. soldiers stationed overseas.

Ferdaus was arrested Wednesday in Framingham when undercover federal agents delivered materials he had requested for his alleged plan, including grenades, six machine guns and what Ferdaus believed was C-4 explosive.

(CNN) — A gunman opened fire Tuesday at a Carson City, Nevada, IHOP restaurant, killing three people and wounding six others before turning the gun on himself, police said.

The suspected gunman is not expected to survive, said Sheriff Ken Furlong of the Carson City Sheriff’s Office.

The shooting began shortly before 9 a.m., according to Furlong. When authorities arrived, those who called in the incident identified the shooting suspect as a man lying wounded in the parking lot.

Two victims were found dead at the scene, and seven others were taken to a hospital for emergency surgery. One of the wounded died during surgery, Furlong said. He did not know which hospital was treating the suspect.

OSLO (Reuters) – A suspected far-right gunman in police uniform killed at least 84 people in a ferocious attack on a youth summer camp of Norway’s ruling Labor party, hours after a bomb killed seven in Oslo.

Witnesses said the gunman, identified by police as a 32-year-old Norwegian, moved across the small, wooded island of Utoeya in a lake northwest of Oslo Friday, firing at young people who scattered in panic or tried to swim to safety.

DES MOINES, Iowa — An eight-term congressman from Iowa helped fight off an armed man who invaded his farm house in Decatur County and attacked his daughter on Saturday night, according to a statement from his office. The attack occurred around 10:45 p.m. on Saturday at a farm in Lamoni,
where Rep. Leonard Boswell, a 77-year-old Democrat who represents Iowa’s
third congressional district, was spending the weekend with his wife,
daughter and grandson.

WASHINGTON — Americans from Washington to California are marking Memorial Day with parades, barbecues and special tributes tied to the 10th anniversary of the Sept. 11 terrorist attacks.

An annual holiday honoring the nation’s war dead was infused with new meaning this year, coming just months before the 10-year anniversary.

Atlanta, Georgia (CNN) — Roland Marbaugh wrote 509 pages of his tales of war — from the swampy Solomon Islands in World War II to the frozen Chosin Reservoir in Korea.

His son typed them all up on an electric typewriter in the 1980s but unpublished, Marbaugh’s stories remained largely in his mind. Until now.

Marbaugh’s story will soon be among 600 others on Witness to War, a virtual library of Americans in combat. When his testimony is posted in a few days, viewers will be able to hear the former Marine captain, now a spry 91, recount harrowing tales with photographic precision.