on the heels of
ありえないようなことがDCで起きました。Amazon.comでテレビを注文したはずが、届けられたのは半自動式ライフルだったのです。
on the heels ofというイディオムは、以前、Koyamamoto先輩が取り上げられていますが（http://d.hatena.ne.jp/A30/20110120/1295516833）、「…のすぐ後について, …に引き続いて」という意味です。かかとを表すheelsが「〜したての」「〜が起きたあとの」という意味で比喩的な意味で使われたこの言い回しは確かにイメージがしやすいものです。ここでは「２件の乱射事件が起きた直後だっただけに」という意味に解釈できます。（Minnesota）
Washington man orders TV, gets assault rifle instead
Police in Washington are looking into how a local resident who ordered a color TV set via Amazon.com ended up with a high-powered semi-automatic assault rifle instead.
Seth Horvitz, who lives in the northeast quadrant of the US capital, said he contacted police immediately after a parcel delivery service left the military-style SIG Sauer SIG716 at his apartment door. They were a little confused at first. They've never seen anything quite like it, he told Fox 5, a local television station.
They just took my information and then said: 'We'll handle this weapon because it's illegal to keep here.' It's illegal to transport in a car, so it can't be returned. While the box was addressed to Horvitz, who had ordered a flat-screen television from a third-party retailer via Amazon.com, an invoice inside the box suggested the gun was supposed to go to a Pennsylvania gun shop.
A spokesman for Washington's Metropolitan Police Department told AFP on Wednesday that the case -- which comes on the heels of two mass killings in the United States in less than a month -- remains under investigation. On its website, the US subsidiary of SIG Sauer, a major European firearms manufacturer that supplies guns to many US police forces, says the SIG716 is the rifle of choice when you require the power of a larger caliber carbine.
We've seen in recent weeks the tremendous damage these guns can do, said Dan Gross, president of the Brady Campaign to Prevent Gun Violence, which campaigns for greater gun control in the United States. We have to be better than a nation where assault weapons are so prevalent and can so easily end up in dangerous hands, he said in a statement. It's deeply disturbing.
