Voters in Washington state approved one of the toughest gun control laws in the country. The measure increases the age limit to buy a pistol or semi-automatic assault rifle from 18 to 21, imposes a 10-day waiting period for purchases, and increases background checks.

According to CBS affiliate KIRO-TV, Initiative 1639 passed with 60 percent approval. In addition to the change in purchase age, the initiative prohibits anyone who is not a Washington resident from buying a semi-automatic assault rifle in the state. In addition, it holds gun owners responsible for safely storing their firearms.

Supporters said the goal is to make schools and communities safer by putting checks in place to keep weapons out of dangerous hands. One of the initiative's supporters is Paul Kramer, whose son was wounded in a shooting at a party in Mukilteo, Washington, in 2016. The gunman legally purchased the weapon used in the shooting when he was 19.

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"If Initiative 1639 had been in place in 2016, he would not have been able to purchase the semi-automatic assault rifle that allowed him to seriously injure my son and kill three of his close friends," Kramer said in September.

Opponents argued the law puts people at risk by restricting access to guns for self-defense.

Another measure that won approval in Washington is Initiative 940, which makes it easier to prosecute police for negligent shootings. It aims to improve police training in de-escalation tactics and eliminates a requirement that prosecutors prove officers acted with malice to get a conviction in negligent shootings.

Research released earlier this year found strong state firearm laws were associated with lower rates of firearm-related homicide. However, little data exists on the impact of gun control laws because in 1996, Congress passed a law limiting the U.S. Centers for Disease Control and Prevention's ability to study gun violence.