According to news broadcasts on the Panamanian television station TVMax, Panamanian international Alberto Quintero is close to signing with D.C. United. While I have not been able to see the broadcast myself, I have talked to some people in Panama who confirm that it was on the air. Given that, I will let slide my typical rule that I must have a link to a news story; as always, take all reports of soccer contracts with a grain of salt.
Quintero currently plays for Chorrillo F.C. in Panama, the club with which he started. After three years with Chorrillo, Quintero moved to Spain and started playing with an amateur team, Torrellano Illice CF, and helped them earn promotion into the Tercera División. He then played a season for FC Cartagena in the Segunda División, the second division of Spanish soccer, and played in 19 games. After that season he moved to Ontinyent CF, in the Segunda División B, before returning to Chorrillo F.C. and going on loan to Independiente Medellín in Colombia. He helped lead Chorrillo to the 2012 Apertura title.
His Spanish language Wikipedia entry seems to say that he is a central midfielder, but his highlights and his size seem to indicate that he is more of a winger. His YouTube highlight video is slightly different than others that we have seen, especially since the first half of it is Quintero's highlight's from Panama's Gold Cup match against the United States. He seems to be getting hacked to the ground a good deal by the United States defense, but I do like his move to just completely get around Clarence Goodson.