A woman reacts during a minute of silence held at a memorial in front of Brussels' Stock Exchange on Place de la Bourse (Beursplein), March 24, 2016.

A child looks on during a vigil at the Belgium Consulate, March 23, 2016, in Montreal, to mourn the victims of the attacks that occurred in Brussels.

People look at messages written in chalk on a wall on the Place de la Bourse (Beursplein) in central Brussels, March 24, 2016, in tribute to the victims of the Brussels attacks.

People attend a street memorial service near the old stock exchange in Brussels following Tuesday's bomb attacks in Brussels, Belgium, March 23, 2016.

A woman holding a Belgian flag joins in singing and chanting at the Place De La Bourse in honor of the victims of terrorist attacks on March 23, 2016 in Brussels.

Employees at Zaventem airport take part in a silent walk to commemorate the victims of a terrorist attack in Brussels, March 23, 2016.

Teresa Mancheno, center, a maintenance worker at Newark Liberty International Airport, prays during a vigil honoring the victims of the attacks in Belgium, March 23, 2016, in Newark, N.J.

A woman and two children visit a memorial for the victims of the bombings at the Place de la Bourse in the center of Brussels, March 23, 2016.

Belgium's King Philippe and firefighters lay a wreath in front of the damaged Zaventem Airport terminal in Brussels, March 23, 2016.

Visitors to the Washington Monument walk under flags flying at half-staff early Wednesday, March 23, 2016, honoring the victims of the Brussels attacks, in Washington. In the background is the Lincoln Memorial.

People light candles during a memorial ceremony at Hanoi Tower in Hanoi, Vietnam, March 23, 2016, in tribute to victims in terrorist attack in Brussels.

People light candles and offers flowers asking for the "Justice for Brussels" during a memorial event along a main street in Quezon city, metro Manila, Philippines, March 23, 2016.

Flowers and candles are seen on the steps at the Belgian embassy in tribute to victims of Tuesday's attacks in Brussels in Berlin, Germany, March 23, 2016.

People hold a minute of silence around a makeshift memorial at Place de la Bourse in Brussels, March 23, 2016.

A man reacts at a street memorial following Tuesday's bomb attacks in Brussels, March 23, 2016.

Supporters for victims of the Brussels terrorist attacks gather to show their solidarity during a vigil and moment of silence in San Francisco, Calif., March 22, 2016.

The colors of the Belgian flag are projected on the courthouse in Lyon, France, in tribute to the victims of today's Brussels bomb attacks, March 22, 2016.

A young girl lights a candle at the Place de la Bourse following today's attacks, March 22, 2016 in Brussels.

Ukrainian servicemen hold torches in front of floral tributes during a ceremony to honor the victims of the Brussels attack in front of the Belgian embassy in Kiev, March 22, 2016.

People hold up a banner as a mark of solidarity at the Place de la Bourse following the attacks on March 22, 2016 in Brussels, Belgium.

A woman lights a candle as people gather to leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium.

Two soldiers from the Belgian Army patrol outside EU headquarters as EU flags fly at half mast after explosions in Brussels on March 22, 2016.The attack prompted a lockdown of the Belgian capital.

Floral tributes, candles, notes and a drawing by French cartoonist Plantu are displayed at the Place de la Republique in Paris in tribute to the victims of the Brussels attack, March 22, 2016.

A local holds a paper national flag of Belgium at Beursplein square following the attacks on March 22, 2016 in Brussels, Belgium.