Interesting excerpt from
http://www.ku.edu/history/index/europe/ancient_rome/E/Gazetteer/People/Robert_E_Lee/FREREL/1/24*.html regarding then Lieutenant Colonel Robert E. Lee's involvement with Juan Cortinas. Wasn't only the Rangers after him.
The situation in the North had improved to such an extent by March 15 that Lee left San Antonio on that date for the Rio Grande to deal with Juan Cortinas. This man had been a bandit and desperado for ten years and in various ways had defied the Texas authorities. With something more than fifty men, on September 28, 1859, he had seized the town of Brownsville, where there were no United States troops and only a few American citizens. Cortinas had a free hand to murder and to rob, and then, for a time, he played hide and seek on both sides of the Rio Grande. On October 22 he worsted an irregular force sent out against him, and captured two light field-pieces from it. This success greatly emboldened him and gave to his activities almost the appearance of an insurrection. On the night of December 5, however, Lee's old West Point acquaintance, Major S. P. Heintzelman, arrived at Brownsville with 117 men, took over the demoralized Texas Rangers, and on December 27, near Rio Grande City, attacked and routed Cortinas's bandits. Thereafter the thieving band disintegrated rapidly. With the leader on the run and his followers dispersed, Lee anticipated no trouble, "but," he wrote Custis, "there are so many contradictory reports that I think it better to see for myself, that I may if possible give quiet there and rest to the authorities at Washington."
Accompanied by a single company of cavalry, Lee pushed on toward Ringgold Barracks, but turned to the southwest and made for the Rio Grande in the vicinity of Eagle Pass, when he heard a rumor that Cortinas was in that quarter. From Eagle Pass, Lee and his men rode down the river to the barracks, where they arrived on March 31. Once on the Rio Grande, Lee saw it would be impossible to catch Cortinas, or to prevent his return, unless the Mexican Government also took action against the bandit. Lee had been authorized to demand co-operation and to enter Mexico, if need be, in pursuit of Cortinas, so he called the Mexicans to their duty in this letter, written in a style he probably had acquired thirteen years before from General Scott:
Hd. Qrs. Ringgold Barracks, 2d April, 1860.
His Excy. Andres Trevino,
Govr. of State of Tamulipas, etc.,
Victoria, Mexico.
Sir: In consequence of the recent outrages of Cortinas and his followers upon the persons and property of American citizens, I have been instructed by the Sec'y of War of the U. S. to notify the authorities of Mexico on the Rio Grande frontier, that they must break up and disperse the bands of banditti which have been concerned in these depredations and have sought protection in Mexican territory. Further, that they will be held responsible for the faithful performance of this plain duty on their part. I have, therefore, the honor to request that your Excellency will cause to be dispersed any bands within the States under your jurisdiction, having for their object depredations upon American soil.
From Ringgold Barracks, on April 3, Lee conducted a careful inspection of the lower Rio Grande valley and not until April 11 did he reach Fort Brown. On the way he had some correspondence with the authorities at Reynosa, and later he received a protest from General G. Garcia of the Mexican army, over the action of some of the Texas Rangers, who had gone across the river into Mexican territory at that point, forty miles west of Matamoras, in quest of Cortinas. Lee answered with some sharpness:
Hd. Qrs. Fort Brown, Texas, 12th April, 1860.
Gen'l G. Garcia,
Commr. in Chief of the line of the Bravo,
Matamoras, Mexico.
Gen'l: I had the honor to receive your letter of the 6th inst. on my way to this place, and postponed replying till my arrival. I regret that you consider the visit of Captain Ford of the Texas Rangers to the town of Reynosa, a cause for complaint, as that officer in his official report of the occurrence supposed he was acting in accordance with your sanction and the general understanding between yourself and Major Heintzelman, commanding the U. S. troops on the Rio Grande, viz., that the outlaw Cortinas and his band should be pursued and arrested wherever found.
I was gratified to learn from the authorities of the city of Reynosa and am pleased to have it repeated in your letter of the 6th that the authorities and public force of Mexico, under the orders of the superior authorities, will pursue and punish Cortinas and his followers; as the vindication of the violated laws of the United States will conduce to the restoration of quiet on our frontiers, and of amicable feelings between the two countries. For the attainment of this object I shall employ, if necessary, all the force in this Department, and I beg leave to inform you that I have been directed by the Honble Sec'y of War of the U. S., to notify the Mexican authorities on the Rio Grande, that they must break up and disperse the bands of banditti concerned in the outrages against the persons and property of American citizens. I shall therefore consider it my duty to hold them responsible for its faithful performance. As this agrees with the orders of the superior authorities of your own Govt. and I am sure is in accordance with your own sentiments, I feel confident of your cordial cooperation in the only means of preserving peace between the two countries. I have been informed that there are now in Matamoras persons that were engaged with Cortinas in his depredations upon American soil, ready, if opportunity favors, to renew these aggressions. If this is the case, I shall expect as an evidence of the friendly relations between the Govts. of the U. S. and Mexico, that they be apprehended and punished agreeably to the orders of the superior authorities of Mexico.
Lee did not think the Mexicans would act against Cortinas, and though the bandit was reported to be 135 miles away, moving into the interior, Lee would have crossed the river and would have started in pursuit if he had believed his feeble horses could have found food in the country they would have had to cover. As time passed and Lee heard nothing more of the bandit, he decided that Cortinas had left the Rio Grande, and he accordingly planned to return to San Antonio. The day before he had arranged to start, however, he got a report that Cortinas was back on the Rio Grande. To trap him Lee sent two companies across the river, only to find, once again, that rumor outrode the bandit. More correspondence with the Mexican authorities followed. Finally they promised to arrest Cortinas, and Lee set out for San Antonio. He covered the 264 miles between May 8 and 17. Two months later Lee was able to report that even rumors of Cortinas's presence on the north bank of the Rio Grande had ceased and that he proposed to withdraw some of the troops from unhealthy districts on the river.
