The leads in the two stories are about the same subject, of course, but approach it in different ways. The first day story just states that robbers broke into the museum and stole artifacts. The second day story said that not only did robbers break in, but starts out talking about the manhunt that is taking place to find the robbers.
The first day story is three sentences long. Each sentence is attributed to the police and states what happened regarding the burglary.
The second day story is 13 paragraphs long and discusses not only the actual burglary, but also discusses a burglary that happened in Greece last month, budget and staffing cuts to the museum, the resignation of an official, and touches on the lighting of the Olympic flame ceremony, which is going to be held at the site in May.
The first day story very clearly is attempting to get the facts of the story out as quickly as possible, as opposed to trying to write a riveting story. The second day story tells the reader more information about why they should care and the impact this robbery is having on people.
The second day story could very well be a response to other news organizations. The Huffington Post also had a very detailed account of the robbery along with discussion about the budget cuts to the museum and the 2013 Olympics. It certainly would not be very competitive of CNN to write the initial story, which was 3 sentences long, and leave it at that because readers interested in the story would have to move to another news organization to find the information they want.