Story highlights

NEW: British foreign secretary: "It's more likely than not" that a bomb brought down the plane

Russia: The remains of more than 100 victims have been identified through DNA testing

Some intelligence used to assess what happened to jet came from Israel, sources say

CNN  — 

ISIS’ affiliate in Egypt says it brought down Metrojet Flight 9268. And U.S. officials are more confident that terrorists bombed the Russian plane, killing all 224 people aboard.

But key questions remain: If terrorists did plant a bomb, how did they do it? And what could prevent that from happening again?

Here’s the latest on what we know about the disaster:

The bomb theory

Several senior U.S. intelligence, military and national security officials have told CNN about the growing confidence that terrorists bombed the plane.

One official said it was “99.9% certain.” Another said it was “likely.”

The plane was headed from the Egyptian resort city of Sharm el-Sheikh to St. Petersburg, Russia, on October 31. But not long after takeoff, it disintegrated midair and crashed in the Sinai Peninsula.

British Foreign Secretary Philip Hammond told CNN’s “The Situation Room” on Monday that his government still believes “it’s more likely than not” that an explosive device caused the plane crash.

“Obviously, we won’t know absolutely for certain until the final analysis of the wreckage has taken place,” he said. “That could take some time.”

British officials, he said, “acted on a precautionary basis” using all the evidence they had when they decided last week to suspend flights to Sharm el-Sheikh, he said. He declined to detail what intelligence led to the move, but said the decision – which came a day before Egypt’s President was scheduled to visit London – wasn’t made lightly.

“We’re sharing what we can. But some intelligence is sensitive, and clearly we don’t share the most sensitive intelligence. What people like the Russians and the Egyptians will very clearly be able to see is the conclusions that we have reached. … Clearly, that was not a comfortable decision for us to make. We made it on the basis of the information,” he said.

Egyptian officials, who are leading the main crash investigation, haven’t expressed as much confidence in the bomb theory.

“All the scenarios” are still on the table, said Ayman al-Muqaddam, the head of the investigation.

“We don’t know what happened exactly,” he said.

The Egyptians aren’t the only ones involved. Experts from Russia, France, Germany and Ireland – countries that are connected in various ways to the Airbus A321-200 that crashed – are also investigating.

Kremlin spokesman Dmitry Peskov confirmed to reporters Monday that the United Kingdom provided Russia with data on the downing of the jet.

Meanwhile, talks between U.S., Russian and Egyptian officials about the potential scope of American assistance in the investigation are ongoing. U.S. law enforcement officials told CNN that the FBI is already offering limited support but has no plans to send a team to the region.

Russian state news agency RIA Novosti reported Monday that Russian experts may receive the first forensic analysis data potentially revealing traces of explosive substances on the wreckage as early as Thursday. But more definitive conclusions could take longer, according to the report.

Sources: Israel provided intercepts

At least some of the intelligence intercepts being used to assess what happened to the jetliner came from Israeli intelligence, according to a U.S. official briefed on the intelligence as well as a diplomatic source.

What we know, don’t know

The communications were captured by Israeli intelligence focused on the Sinai and passed along to the United States and Britain, the sources said.

Israeli officials would not comment on the claims.

Muqaddam said Egypt was not given any information or evidence tied to reports suggesting a bomb took down the flight, and he urged the sources of the reports to pass along related evidence to Egyptian investigators.

ISIS chatter analyzed

The belief that a bomb was most likely to blame centers, to a large extent, on British and U.S. intercepts of communications after the crash from the Sinai affilate of the Islamic militant group ISIS to ISIS operatives in Syria, officials said.

DHS chief seeks to reassure American fliers after crash

The Sinai affiliate has publicly claimed responsibility for downing the plane, but so far hasn’t explained how it was done. That’s prompted questions about the claim among observers, considering ISIS’ tendency to publicize its acts for propaganda value.

The ISIS messages monitored by British and American intelligence agencies are separate from the group’s public claims, a U.S. official has said.

The two Western countries have been analyzing the specific language in the chatter to determine to what extent the operatives were talking about the type of bomb and detonator used, and whether that language was a true representation of what happened, one official told CNN.

Several officials said it’s the specificity of the chatter that has contributed to the U.S. and British view that a bomb was most likely used.

Bergen: Why ISIS is on a roll

Mysterious noise

European investigators who analyzed the plane’s cockpit voice recorder and flight data recorder say the crash was not an accident, CNN affiliate France 2 reported.

The investigators said the cockpit voice recorder indicates an explosion, and the flight data recorder shows the blast was not accidental, the affiliate said.

But Muqaddam, the head of the investigation, did not echo those details.

He confirmed a noise was heard in the final second of the cockpit recording as the aircraft was on autopilot and ascending. But he offered no description of the sound, saying a specialized analysis would be carried out to identify it.

The crash might have been caused by a lithium battery or a mechanical issue, Muqaddam said.

He also said that bad weather has hampered the investigation.

More victims identified

The remains of more than 100 victims have been identified through DNA testing, Russian Deputy Prime Minister Olga Golodets said, according to RIA Novosti.

Most of the passengers were Russian. The others were of Ukrainian, Belarusian or unconfirmed citizenship.

Russian media said the disaster created many orphans because many parents left their children with relatives as they went on vacation to Sharm el-Sheikh.

Opinion: What’s at stake for Putin in investigation

CNN’s Tim Hume, Elise Labott, Oren Lieberman, Salma Abdelaziz, Olga Pavlova, Radina Gigova, Ian Lee, Sarah Sirgany and Catherine E. Shoichet contributed to this report.