The story I will look at is by the Associated Press. http://www.nytimes.com/2013/02/11/us/2-men-held-in-shooting-of-hadiya-pendleton.html?ref=us&_r=0
The story is short, and there are only two sources listed. The first is a police spokeswoman, who is clearly named in the story, Melissa Stratton. The second is simply "the police."
The sources are scattered throughout the story, and it is made clear that the majority of the information is directly from them-- other than the third paragraph which states some information that makes the assumption that we have heard about the story before-- it's referencing past stories.
The information is from people. The reporter sets up the attribution by first introducing the source as "a police spokeswoman," and then in the second paragraph stating her name. The second source is simply "the police," and doesn't have any more of a lead-in or introduction. It is effective, because the story is short and doesn't need a ton of different sources to make its point. I think even having 3 sources would have started to muddle it.